1. Field of the Invention
The present invention relates to a carbide-derived carbon prepared by thermal treatment in a vacuum and a method of preparing the same. More particularly, the present invention relates to a carbide-derived carbon and a method of preparing the same, wherein a carbide compound is thermally treated in a vacuum so that carbide particles are pretreated into a high-density agglomerate to obtain a vacuum-treated carbide compound that is then thermochemically reacted with a halogen element-containing gas so as to extract the element other than carbon, giving a carbide-derived carbon.
2. Description of the Related Art
Lithium ion secondary batteries for use in mobile phones, personal digital assistants (PDAs), digital cameras, camcorders, etc. are configured in the form of a chemical battery system using an oxide cathode material and a graphite anode material. Such electrode materials are prepared into a slurry together with an appropriate binder and conductor to fabricate a cathode plate and an anode plate, which are then wound or stacked with a separator to form a core cell, followed by encasing the core cell, thereby manufacturing a lithium ion secondary battery having a cylindrical, rectangular, or pouch shape.
Thorough research is ongoing into enhancing performance of lithium ion secondary batteries, including capacity and energy density. To this end, methods of enhancing performance through design improvements and also through material developments and improvements have been devised. However, optimal performance enhancement is considered to be due to development of electrode active materials.
When lithium metal is used for an anode to correspond to a lithium transition metal oxide as the cathode material, high energy density and low self-discharge rate may be exhibited, but serious problems are generated during the actual charge/discharge of batteries. First, lithium metal is dissociated into lithium ions in an electrolyte during discharge and then deposited as lithium metal at an anode during charge. As such, there are many cases where the deposited metal is not restored into lithium in a uniform planar phase before discharge but may be formed into needle-shaped crystals, twig-shaped crystals, or particle crystals. As the charge process progresses, such crystals are continuously grown and ultimately reach the cathode through the separator, undesirably causing an internal short circuit or deteriorating cycle properties. Furthermore, a large charge current facilitates crystallization, and thus cycle properties may remarkably deteriorate during quick charge.
Second, lithium metal may sufficiently exhibit high energy density properties of lithium at low load, whereas the anode utilization may decrease during high-load discharge, undesirably lowering the energy density. On the other hand, cycle properties may be comparatively good during high-load discharge but may remarkably decrease during low-load discharge. The use of lithium metal for the anode makes it very difficult to balance load properties and cycle properties.
Hence, lithium ion secondary batteries have been developed to employ, as an anode material, a carbon material having electrode potential similar to that of lithium metal while enabling electrochemical interlayer intercalation/deintercalation of lithium ions, instead of using lithium metal as the anode due to the aforementioned problems. As for the anode, the use of carbon material able to form an interlayer compound may result in only movement of lithium during charge/discharge, and the original shape of the anode material is maintained, thereby increasing the lifetime of the battery. Although a graphite material having advantages as above has been receiving attention as the anode active material, it has theoretical capacity limitation of 372 mAh/g, and thus anode materials that may replace currently used anode materials are under study.
Accordingly, a material for an electron emission source to emit electrons may include a carbon material, for example, carbon nanotubes having superior conductivity, field concentration effects and field emission properties, and low work function. However, carbon nanotubes are typically provided in the form of fiber having high field enhancement factor, and a material having such a shape has many defects in terms of material uniformity and lifetime. Also, when made into paste, ink or slurry, carbon nanotubes in fiber form may incur poor process problems compared to other materials in particle form. Moreover, carbon nanotubes are undesirable because materials therefor are very expensive.
With the goal of solving the problems with carbon nanotubes, thorough research into carbide-derived carbon is being carried out. However, a carbide-derived carbon resulting from simply thermochemically reacting a carbide compound with a halogen element-containing gas does not have a uniform shape because crystalline graphite and amorphous carbon coexist. Furthermore, limitations are imposed on manifesting stable performance as the secondary battery anode material due to formation of pores between amorphous carbon particles and formation of mesopores due to high temperature.